1. Field of the Invention
The present invention relates to a technology to perform exclusive control for using a shared resource to which a plurality of data access devices can access.
2. Description of the Related Art
As this type of technology, the technology disclosed in Japanese Patent Application Laid-Open No. H5-265985, for example, is known. In this technology a central processing unit (server), which is connected between a plurality of distributed processing units (clients), and a shared disk device, controls access of the plurality of distributed processing units to the shared disk device. Specifically, when the central processing unit receives a file update request from a distributed processing unit, the central processing unit sets the target shared file in lock status, then monitors the duration time of the lock status by a time counter, and detects if the distributed processing unit, which requested the update of the file, is down when time is up before the update of the shared file ends, and if down, the lock status is forcibly cleared.
According to Japanese Patent Application Laid-Open No. H5-265985, it is detected whether the distributed processing unit is down, and the lock status of the shared file is forcibly cleared if down. In Japanese Patent Laid-Open No. H5-265985 however, nothing is disclosed or suggested on how to detect whether a distributed processing unit is down.
Also according to Japanese Patent Laid-Open No. H5-265985, one central processing unit detects whether the plurality of distributed processing units are down, so if an abnormality occurs to the central processing unit itself, exclusive control of use of the shared disk device cannot be performed even if the plurality of the distributed processing units are not down.